Systems for providing neurostimulation via an implanted probe are used for treatment of disorders such as chronic pain, Parkinson's disease, tremor and dystonia. Neurostimulation is used for stimulating neural tissue in the brain, the spinal cord and peripheral nerves. In the following, neurostimulation of brain tissue will be discussed. However, the system and method according to the invention can also be used for neurostimulation of, e.g., the spinal cord and peripheral nerves. The probe is surgically implanted in the brain, close to the brain tissue that is to be stimulated. When using neurostimulation it is important to stimulate the tissue that needs stimulation and to avoid stimulation of other nearby tissue. Correct placement of the probe thus is an important step in a successful neurostimulation treatment. In known systems for planning implantation of the probe, imaging techniques such as Magnetic Resonance Imaging (MRI) are used to visualize the target region. The surgeon tries to locate the structures that need stimulation and tries to define a surgical plan to implant the probe in the identified structure.
In a pending patent application of the same applicant as the present patent application, with application number EP10159853.0 (internal reference PH014693EP1) an example of a system for planning neurosurgical operations is described. The system described therein uses different imaging techniques to determine a surgical trajectory avoiding the critical neural structures. Said system could be useful for planning a trajectory for implanting a neurostimulation probe, but cannot be used for determining an optimal location for successful neurostimulation treatment.
A known way of trying to stimulate the correct tissue region is to implant a probe with a plurality of electrodes and to select only a subset of these electrodes so as to stimulate only specific tissue regions. This is, e.g., described in U.S. patent application US 2008/0215125. This U.S. application describes a probe with a plurality of electrodes which is implanted close to the region of interest. Electrical charges are supplied to a subset of these electrodes to selectively stimulate specific tissue regions. Also in U.S. Pat. No. 7,442,183 a subset of a plurality of electrodes is activated to steer an electrical field to the target region. In U.S. Pat. No. 7,442,183, it is noted that the selective activation of a subset of the electrodes makes the precise probe location relative to the target structure less critical.
Although the use of electrode arrays does enable steering 3D electric field distributions to specific tissue regions, the full range of 3D stimulation patterns that can be created is still dependent on the exact position and orientation of the probe. For optimal therapy delivery options and tuning flexibility thereof an optimal lead positioning should be arranged in the therapy planning phase.